Manufacture of fluorine-containing polymers



YIELD POLYMER June ,1 A. DITTMAN EIAL 2,337,505

MANUFACTURE OF FLUORINE-CONTAINING POLYMERS I Filed May 11. 1954 3Sheets-Sheet 2 BIO .005 .03 .02: .029 .037 .045 .055 .oel .069 .011 .085

(500 Ram. ream-1x 0) MOLAR Kzsaoo FIG.2

a :0 l2 l4 l6 I8 20 22 -24 (500 REM. s -1:1 0) INVENTORS HERBERT J.PASSINO 3 BY ALBERT DITTMAN J N m. WRIGHTSON ATTORI EYS United tatsMANUFACTURE OF FLUORINECONTAlNING PGLYMERS Albert L. Dittman, NorthBergen, and Herbert J. Passino, Englewood, N. J., and John M. Wrightson,Whittier, Califl, assignors, by theme assignments, to Minnesota Miningand Manufacturing Company, St. Paul, Minn a corporation of DelawareApplication May 11, 1954, Serial No. 428,972

Claims. (Cl. 266-921) This invention relates to the manufacture offluorinecontaining polymers. In one aspect this invention relates to thepolymerization of halogenated olefins containing fluorine to producepolymers containing fluorine. In another aspect the invention relates tothe polymerization of perhalo olefins in the presence of an aqueoussuspension medium to produce a polymer. In still another aspect theinvention relates to the polymerization of trifluorochloroethylene inthe presence of an aqueous suspension medium to produce a normally solidpolymer of high chemical and physical stability. This application is acontinuation-in-part of application Serial No. 213,524, filed March 2,1951, now U. S. Patent No. 2,689,241, and application Serial No. 61,082,filed November 19, 1948, and now abandoned.

Various olefins containing fluorine may be polymerized under suitableconditions to produce polymers in the form of liquids, waxes and solids.Under suitable reaction conditions, trifluorochloroethylene, forexample, polymerizes to produce a range of molecular weight polymersuseful for various purposes. These polymers, produced fromtrifluorochloroethylene, are relatively inert chemically and have goodphysical properties in general. The oily polymer oftrifluorochloroethylene may be used as a lubricant or insulating medium.The waxes of trifluorochloroethylene are also useful in making uplubricating compositions and for impregnating various materials to makethem chemically resistant. The solid polymer of trifluorochloroethylenein its high molecular weight stage has the characteristics of athermoplastic and is useful for a variety of purposes for which plasticsmay be used.

The present method of polymerizing trifluorochloroethylene is by a bombtype reaction at a relatively low temperature. Thetrifluorochloroethylene monomer is introduced into a bomb type reactorwhich is maintained at a temperature of about 17 C. for a period ofabout seven days. The monomer is converted to a porous plug of solidpolymer in the reaction vessel with approximately 30 percent yield ofpolymer based on the monomer charged. The unreacted monomer is includedin the interstices of the porous plug and may be removed therefrom byheating the plug in the reaction vessel under subatmospheric pressure sothat the monomer is evaporated. After the monomer is evaporated, theplug is removed from the reaction vessel and broken into chips orgranules for shipping, molding, etc.

The object of this invention is to provide a commercially feasibleprocess of polymerizing halogenated olefins containing fluorine toproduce a polymer in relatively high yields.

Another object of this invention is to provide a process in which arapid and economical polymerization of perhaloolefins, such astrifluorocholoroethylene, can be effected.

Another object of this invention is to provide an ac- 2337,55 PatentedJune 3, 1958 celerator for increasing the yield and shortening the timeof polymerization of halogenated olefins.

Various other objects and advantages of the present invention willbecome apparent to those skilled in the art from the accompanyingdescription and disclosure.

As herein defined, polymerization refers to the polymerization of asingle monomer and also to the copolymerization of unlike monomers toproduce polymers.

According to this invention, a substituted ethylene containing at leasttwo fluorine atoms, preferably at least one fluorine atom per carbonatom of the aliphatic portion of the substituted ethylene, ispolymerized in the presence of an aqueous suspension medium undersuitable conditions of temperature, pressure, residence time andpromoting agents to produce a polymer, either liquid, wax or solid. Thepolymerization process of this invention may be effected in either abatchwise or continuous manner. The monomer is admixed with the aqueoussuspension medium in a suitable polymerization zone which is maintainedat the appropriate conditions of polymerization and under sufiicientpressure to maintain the aqueous solution as a liquid under theconditions of polymerization. The monomer and water are agitated bysuitable means in the reaction zone so as to intimately disperse themonomer in the aqueous suspension medium. The monomer and polymer aresubstantially insoluble in the aqueous dispersion medium. The separationof the polymer from the 'water phase may be effected by settling anddecantation, by filtering, by centrifuging, by evaporation; or byvarious other conventional methods, depending upon whether the polymeris in a liquid or solid state.

The present invention is particularly applicable to thehomopolymerization oi perfluorochloro olefins, such astrifluorochloroethylene. However, the invention contemplates thepolymerization of various halogenated olefins. For example,perfluorobutadiene, perfluoropropene, phenyltrifluoroethylene, alphamethyl phenyl difluoroethylene, perfluoro acrylonitrile,perfluorostyrene, perfiuorocyclobutene, perfluorocyclobutadiene,tetrafluoroethylene, vinylidene fluoride, trifluoroethylene anddifluorodichloroethylene. As previously mentioned, the invention appliesto the copolymerization of these monomers, as well as theirhomopolymerization. For example, the invention applies to thecopolymerization of trifluorochloroethylene and tetrafluoroethylene, of-trifluorochloroethylene and vinylidene fluoride,trifluorochloroethylene and vinyl fluoride, trifluorochloroethylene andvinyl chloride, trifluorochloroethylene and vinylidene chloride,trifluorochloroethylene and perfluoropropene, trifluorochloroethyleneand trifluoroethylene, and of perfluorobutadiene and perfluorostyrene.In these copolymerizations, the second monomer is also preferably afluorinated olefin and preferably containing at least two fluorine atomsper molecule. When less than 5 weight percent comonomer is employed, thepolymerization is broadly included within the term homopolymerization.

The quantity of water employed as the aqueous suspension medium isusually between about 0.05 to about 10 times by volume of the quantityof total monomer present in the reaction zone. Preferably, the quantityof water is between one and five times the total monomer in the reactionzone.

The temperatures employed for the polymerization will depend to acertain extent upon the particular monomers being polymerized.

20 to about 1500 pounds per square inch gage, the lower:

In general, the temperatures range pressures being used usually with thelower temperatures of polymerization. The higher temperatures areemployed in the above range for the. production of the liquid polymers,while the lower temperatures are usually employed for the production ofsolid polymers. For example, in the production of solid polymers oftrifiuorcchloroethylene, temperatures between about C. and about 30 C.or 40 C. are preferred, and for producing the liquid polymer of the samemonomer, temperatures between about 75 C. and about 200 C. arepreferred.

Similarly, the time of polymerization will depend upon the particularmonomer being polymerized but, also, upon such factors as thecomposition of the monomer, molecular weight of the ultimate polymer,the temperature of polymerization and the type of promoter and activatorbeing employed. In general, the polymerization time is between aboutminutes and about 50 hours and usually between about 5 and about 35hours.

The aqueous phase type of polymerization for the above monomers usuallyrequires a suitable promoting agent for effecting the polymerization ina reasonable length of time and to produce a polymer of the desiredmolecular weight. These promoting agents fall in three general classes;promoters, activators and accelerators. In almost all instances, apromoter must be used. Such promoters comprise the inorganic peroxides.Examples of suitable inorganic peroxides are the water soluble per xide,such as the perborates, persulfates, perpho-sphate' percarbonates,barium peroxide, zinc peroxide and hydrogen peroxide. Particularlyvaluable are the water soluble salts of the peracids, such as sodium,potassium, calcium, barium and ammonium salts of the persulfuric and perphosphoric acids which may be prepared in the conventional manner byelectrolytic oxidation of salts of the corresponding oxy acids. Suitableconcentrations of the promoter lies within the range of 0.003 molar toabout 0.1 molar. The exact quantity of promoter will depend upon themonomer, molecular weight of the polymer desired and the particularpromoter being employed. For example, in the polymerization oftrifiuorochloroethylene to produce the solid polymer thereof having asoftening point above 200 C., a promoter concentration between about0.003 and about 0.07 molar, or about 0.0l and about 2 percent by weightbased on water, is preferred. Somewhat higher concentrations areemployed for producing the liquid polymer.

Promoters are also preferably used in conjunction with an activator toincrease the yield of polymer. Such activators comprise sodiumbisulfite, sodium hydrosulfite, sodium thiosulfate and trimethylamine,and in general any water soluble reducing agent. These activators aregenerally employed in concentrations similar to the concentration ofpromoter employed. Equal molar amounts of promoter and activator arepreferred.

Buffering agents may be employed also to obtain optimum pH conditions.For example, when an alkaline pH is desired, butters such as borax,disodium phosphate, sodium carbonate, ammonium carbonate, and sodiumacetate may be used. For an acid pH, acetic acid, propionic acid andmoncsodium phosphate may be employed. It is preferred to maintain a pHbetween about 1 and about 4.

In accordance with this invention, it has been found that the yield ofpolymer may be substantially increased and the time of polymerizationmay be substantially decreased by the use of accelerators, suchaccelerators being the ionizable inorganic water soluble salts of anaccelerat ing element which element in its oxidized state is morereadily reducible than the promoter and in its reduced state is morereadily oxidizable than the activator; preferably, the salts of theheavy metals, such as iron, manganese and chromium. Various Watersoluble salts of an accelerating element of the above definition may beemr 4 ployed other than the metals given above. Examples of: theraccelerating elements are cobalt, silver, copper, nickel, molybdenum,and iodine. The accelerating element is introduced into the aqueousreaction mixture in the form of the water soluble salts, preferably asthe low valence form of the accelerating element, and after introductionand dissolution therein the salts ionize. Various salts of theaccelerating element comprise the hydroxides, carbonates, sulfates,phosphates, nitrates and chlorides. These salts of the acceleratingelement are admixed with the reaction mixture in an amount sufficient tomaintain the concentration of the accelerating element or elementsbetween about 1 and about 2000 p. p. 111. based on water. For the bestresults, the concentration of accelerating element or admixtures ofaccelerating elements is preferably maintained between about 5 and about300 p. p. m. in the aqueous phase during the polymerization. In thepolymerization of trifluorochloroethylene in a potassiumpersulfate-scdium bisulfite aqueous system, an iron sulfate is admixedwith the reaction mixture in an amount suiiicient to maintain theconcentration of the accelerating element between about 10 and about p.p. rn. during the polymerization.

It is preferred to maintain the Water phase substantially free fromwater soluble organic compounds, such as alcohols and ketoncs, sincesuch compounds are inhibitors for the polymerization oftrifluorochloroethylene and have a marked adverse effect on thepolymerization reaction and on the characteristics of the productproduced. The use of purified or distilled Water is thus preferred.

In carrying out the process of this invention using an accelerator, thepolymerization is eitected in a vessel or conduit which is not capableof being attacked by the ingredients employed in the polymerization.Suitable corrosive resistant materials useful for construction or liningof the reaction vessel or conduit comprise stainless steel, Inconel,Monel, silver, nickel, glass or iluorinated solid polymers.

In all cases, the liquid in the reaction zone must be vigorouslyagitated to maintain the reactant and promoting agents in intimatecontact. The vigorous agitation of the liquid phase of the reactor maybe obtained by high speed stirring, such as with small propellersconnected by means of a shaft to a high speed electric motor. Fencedcirculation of the liquid phase through orifices or small diameterconduits is also an effective method for achieving intimate mixing ofthe reactant, water and promoting agents. In general, any systemsuitable for obtaining a mechanical dispersion or suspension withoutusing detergents Will be applicable; in most instances detergents beingharmful to the polymerization reaction.

It is within the scope of this invention to disperse finely dividedsolids in the liquid phase as a suspension for the purpose of acting asfillers for the polymer product and for the purpose of forming nucleifor the start of the polymerization. The following are examples of suchfillers: various pigments, such as titanium dioxide, carbon black;clays; asbestos; glass fiber; and other relatively inert solids.

The following runs are offered as a better understanding of the presentinvention and indicate the appropriate conditions of polymerization andexamples of promoters, activators and accelerators. The runs andconditions are not to be considered unnecessarily limiting to thepresent invention.

Table I illustrates typical runs in glass reaction tubes. The weightratio of water to monomer in these runs was about 2.521 and equimolarconcentrations of potassium persulfate and sodium bisulfite was employedunless otherwise noted to the contrary in the right column. Table Hillustrates typical runs in stainless steel reaction bombs. All runswere made at 5 C. for 24 hours except as noted. Figure 1 of the drawingis a graph of percent yield of solid polymer versus molar concentrationof potassium persulfate employing an equimolar quantity sheet and cutinto a strip of A" x X 1 /8.

strip is notched from the top so that the dimension at the notch shallbe X A shall equal /2 grams.

of the sample is increased at a rate of about 1 /z C. per minu isapproached. The no strength temperature is the breaking temperature ofthe sample. Differences of about 5 C. are considered significant.

Figure 4 of the drawings is a diagrammatic illustration of anarrangement of apparatus in elevation for a conhomopolymer from themonomer trifluorochloroethylene. The starting materialtrifluorochloroethylene may be prepared by dechlorinating Freon 113,trifluorotrichloroethane, in the presence of powdered zinc. According topurities accompanying the monomer is introduced into a fractionaldistillation column 4 through conduit 3. Recycled monomer is introducedinto the lower portionof column .4 through conduit 35. In fractionator4, triaction.

TABLE I Best A. no strength temperature one new rrr s m c e m m 868 M eEFF .6 m .26 Mm. mmmmm l H O2 0.0.0.660 m mass wa m m flnmmw OOOOO m r m2 22222 2 1 p nnnn aas. a m m m D... aaaaaNaw fi e ee-nnm 3 NNNNN .N p Fmmmmmm w eeeeeme mm s aaammn. H mmmmmwmmm k wm 7 OOCCCYCS M h h m .rITTTTfi M m aaflffi 0 mmmmmml a e p n e "W OOOOOmO F R 0 dddHHw F mmmmmm m wmmppm 7641781 6 35713110.F 8 m ddmwm n 0 0 0 U l 2 22 2 0 0 0 0 0 0no0d r HwH v HHwwwHH 33333333 m md dm aammwn 4 S SwSS aaSS 3 0850020 088 B 3373.333 a .LlLLL r aa a p n H m m .m mmw wmmmw l r e n E h mp pp mppmw .3 011 4 L M HJRDDPYY DP fi T n B e OPQHUQMMMQODE s 0 u A rmsmamwrrrwmnn o T l N u u w a M "m U nwmnnnmm g s T s 3 .3 .3333322 0807006255265 SC. n n m Kannada/52 9 04 w O u n C w 7777788 99 n e r l m Hn P B N 1. 5 .6 n n 23 u n r m mOm 34M n .Li t 5 S a 79 87 e e %%W QBBUM%H%%ME M%H% P r N n u u N e P t 1681570237473 an I 1 a. 4 6 mmflflmmwfiwn UN2% %M%M%M2M w P T n w 4444%7 u. 55555505555 r 4444444 1 mmmmwmwmw5555555555555 r mm mmmmmwmmwmmmmw s mmw uoouodouoaaoum f T N m s8 77 r s 8 .1 w we mmnwwwnflwwnnmm m nu .n .nn .n mmc mmw 0000000000000m me R N Figure 3 of the drawing is a graph of percent yield of solidpolymer versus reaction time in hours employing of sodium bisulfite and100 p. p. m. FeSO -7H O. Figure 2 of the drawing is a graph of N. S. T.of the solid product of polymerization versus molar concentration ofpotassium persulfate employing an equimolar quantity of sodium bisulfiteand 300 p. p. m. FeSO -7H O.

an equimolar quantity of sodium bisulfite and 300 p. p. m. FeSO -7H O.

Runs 1 to 11 made at 5 C. for 24 hours. To further distinguish the solidpolymer over the corresponding oils and waxes produced with the samemonocharacteristic of a normally solid polymer of the above tinuousprocess for the production of a normally solid preparation havingthermoplastic characteristics.

pends upon the polymerization conditions, such as temthe drawing,trifiuorochloroethylene together with any im- The no strengthtemperature (N. S. T.) is determined in the following manner: Athermoplastic sample of polytrifiuorochloroethylene is hot pressed intoa 5 thick fluorochloroethylene is recovered as an overhead fr mer, thesolid polymer is described by reference to its no strength temperature.

(N. S. T.) of between about 210 C. and about 350 C. is

plastic characteristics of the normally solid polymer are observed at N.S. T. values between about 240 C. and about 340 C. The N. S. T. value ofthe polymer deperature, residence time, concentration and type ofpromoter agents, pressure, etc.

in substantially pure form. Liquid bottoms are maintained at the desiredtemperature of about 86 C. at atmospheric pressure by a conventionalheating or cooling element 6. Undesirable high boiling components orimpurities accompanying the trifluorochloroethylene are withdrawn fromfractionator 4 through conduit 7 for disposal. These undesirablecomponents comprise alcohol and acidic by-products. V aporoustrifluorochloroethylene is removed from the upper portion offractionator 4 and passed through conduit 8 and condenser 9 toaccumulator 11. At least a portion of the trifluorochloroethylene iscondensed by condenser 9 which is maintained at a temperature of about28 C. for atmospheric pressure operations. Condensate is returned fromaccumulator 11 through a conduit 12 to the upper portion of fractionator4 as reflux. Alternatively or additionally to refluxing with condensatein conduit 12, internal cooling means (not shown) may be positionedWithin the upper portion of fractionator 4 for creating an internalreflux.

If only that much of the vapors in conduit 3 are condensed so as toprovide reflux to fractionator 4, the remaining vapors are removed fromaccumulator 11 and are passed through conduits 14 and 16 to a scrubber17 to remove acidic material from the monomer stream. In treater 17 themonomer stream is contacted with a caustic solution of sodium orpotassium hydroxide. This treatment at 17 may also comprise contact withsuitable sorbents, such as silica-gel, phosphoric pentoxide andactivated carbon, for removal of traces of contaminants, such asalcohol. Scrubber 17 is used in order to obtain a monomer of high puritywhich is desirable for the polymerization of trifluorochloroethylene toa solid polymer of good physical and chemical properties.

In case it is desired to treat the monomer in the liquid phase, liquidmonomer is withdrawn from accumulator 11 and passed through conduits 13and 16 to scrubber 17 for liquid-liquid contact with a caustic solution.When this modification is employed, condenser 9 is operated so as tocondense substantially all of the eflluent in conduit 8.

Monomer is withdrawn from scrubber 17 and passed through conduit 18 to aholding tank 19 for storage. In the event the monomer is treated inscrubber 17 in the vapor phase, a condenser (not shown), is provided onconduit 18. From holding tank 19 the purified liquid monomer inappropriate quantities is passed through conduit 21 to a polymerizationreactor 22. Water is introduced into reactor 22 through conduit 24. Theintroduction of water and/or monomer may be intermittent or continuous.A suitable promoter, such as sodium perborate, is also introduced inmeasured quantities by means of conduits 26 and 24. The temperature ofreaction employed may be about room temperature and in order to maintainthe monomer in the liquid phase a pressure of about 100 pounds persquare inch gage is maintained in reactor 22. Liquid monomer and waterare vigorously and intimately admixed in reactor 22 by means of aconventional stirrer 23.

The quantity of water employed in reactor 22 is between about 1 andabout 3 times that of the monomer. A preferred amount of sodiumperborate is between about 0.5 and about 2 weight percent based on themonomer in reactor 22. The average residence time of the monomer inorder to produce solid polymer is between about and about 35 hours. Thesolid polymer forms as a white powder and is removed as a slurry withwater and monomer through conduit 27.

The slurry of solid polymer is passed from reactor 22 through conduits27 and 28 to a stripping unit 31 in which monomer is stripped from theslurry containing polymer by increasing the temperature and/ ordecreasing the pressure of the system. Vaporized monomer is with drawnoverhead from stripper 31 through conduit 32 and may be recycled toreactor 22, or all or a portion thereof may be passed through conduit 35to fractionator 4.

Numeral 33 indicates heating coils for stripping purposes. When passingthemonomer .from stripper 31 to fractionator 4, a condenser is usuallypositioned on conduit 35;

A slurry of polymer and water substantially free from monomer iswithdrawn from stripper 31 through conduit 3 and is passed to aseparator 36. In separator 35, the stripped polymer floats on the waterby virtue of which it is easily separated from the water. Water whichmay contain the promoter or other agents may be recy led to reactor 22through conduits 37 and 38, if desired. it the water containsundesirable contaminants produced by the reaction, the water may bewithdrawn through conduit 37 for disposal.

In some instances the stripping operation in unit 31 re 21y be eiminated and the slurry of polymer, monomer and water passed fromreactor 22 through conduits 27,

2F and 34 directly to separator 36 by proper adjustment of the valves onconduits 28 and 29. When the stripping step is eliminated the polymerwill be heavier than water and will settle to the bottom of separator36.

Separated polymer which may or not contain monomer is passed fromseparator 36 through conduit 39 to drier $1. in drier 41 water and/ormonomer is evaporated and passed through conduit 4-3 for return throughconduits 45, 35 and 32 to reactor 22, or to fractionator 4 throughconduits and 35. If desired, the vapors removed from drier 41 may bevented to the atmosphere; this usually being the case when the strippingstep is employed. On the other hand, when the stripping step is not usedthe vapors in conduit 45 will contain an appreciable amount of monomerand it is preferred under such circumstances to recycle the monomer toreactor 22 or fractionator 4. Dried polymer is removed from drier 41through conduit 42 as a product of the process.

In a modification of the present process in which the? solid polymer maycontain excess amounts of'promoter,

such as sodium perborate, having adverse eifects on the water todissolve the inorganic peroxides contained in the polymer. The solidpolymer is allowed to settle in extractor 44 and may be passed throughconduit 46 to drier 41, if desired. The aqueous solution containing theextracted peroxides or other impurities isremoved from extractor 44through conduit 53 and passed to a stripper 54. In stripper 54 anoverhead fraction comprising an aqueous solution of alcohol and water isobtained and returned to extractor 44 through conduit 52. A bottomsfraction comprising water and impurities, such as inorganic peroxide, isremoved from stripper 54 through conduit 57. Since the inorganicperoxide may be useful as a promoter for the polymerization reaction,the stream in conduit 57 may be returned to reactor 22 by means notshown. reboiler for heating stripper 54 to a sufliciently hightemperature to vaporize the extracting agent. Methyl alcohol may beadmixed in about a 1:1 weight ratio with water for use in extractor 44.

In the event it is undesirable to pass the treated polymer fromextractor 44- to drier 41 because of the presence of alcohol which maycontaminate the monomer, the extracted polymer may be passed throughconduit 57 to drier 43. In drier 48 the alcohol and water contained inthe solid polymer is evaporated by regulation of tem perature therein inthe conventional manner. The vaporized components are removed from drier48 through conduit 51. Dried polymer is removed from drier 48 through aconduit 49 as a product of the process.

The solid polymer recovered at 42 or 49 may be subjected to furthertreatment, such as fluorination, pyrolysis, etc, without departing fromthe scope of this invention. Various modifications and alterations ofthe arrangement Element 56 is a heating coil orof the equipment maybecome apparent to those skilled in the art. Certain pieces of apparatusand auxiliary equipment, such as liquid level controls, flow controls,temperature and pressure controls, valves, pumps, coolers or condensers,heaters and storage vessels have been omitted from the drawing as amatter of convenience and clarity.

The temperature of the reactor may be maintained substantially constantat the desired level by indirect heat transfer with the reactor, such asby immersing the reactor in a liquid bath or by using coils positionedwithin the reactor. The reactor may also be cooled or heated bycontrolling the quantity and temperature of the fresh and/ or recycledwater introduced into the reactor. Because of the high heat transferrate of the Water, temperature control of the reactor is relativelysimple and accurate without wide variations in temperature occurring.

The polymerization may be eifected without the use of a reducing agentand accelerators without departing from the scope of this invention asshown in the following example:

EXAMPLE Approximately 51 parts by weight of monomertrifluorochloroethylene, 120 parts by weight of water, and 4 parts byweight of Na B O -H O were charged to a reactor. The reactor wasmaintained at a temperature of about 25 C. under a pressure sufficientto maintain the monomer in the liquid phase. The contents of the reactorwere vigorously agitated in order to disperse the monomer as finedroplets in the aqueous phase. After about 32 hours, the contents of thereactor were discharged and a fine white powder of solid polymer wasrecovered from the water. The polymer represented a yield based on themonomer charged of better than 30 percent and had good physicalcharacteristics comparing favorably to the polymer produced at lowtemperatures without suspension in water.

The present invention is directed to the use of promoting agents inaqueous dispersion polymerization of substituted ethylenes containingfluorine. Although the invention has been primarily described byreference to the use of a particular accelerator or to the use of asingle accelerator or accelerating element, it is within the scope ofthis invention to use various accelerators alone or in combination oradmixture with each other. The invention is also preferably carried outin a system which is constructed or fabricated of noncorrosive materialsto minimize or prevent the presence of additional ingredients whichwould render control of the concentration of accelerating elementdifiicult. Furthermore, for best results the reactants, promoters anddispersing medium should be of high purity and substantially free fromother elements or compounds. Thus the purification of the monomer inconventional manner and the use of distilled or pure water is highlydesirable.

Various modifications and alterations of the procedures of thisinvention may become apparent to those skilled in the art withoutdeparting from the scope of this invention.

Having described our invention, we claim:

1. A process for polymerizing trifluorochloroethylene to produce anormally solid homopolymer which comprises polymerizingtrifluorochloroethylene monomer in admixture with an amount of waterbetween about 1 and about 10 times the amount of monomer at a pressuresulficient to maintain monomer in the liquid phase in the presence of aninorganic water soluble salt of a weak peracid as substantially the solepromoting agent, and maintaining an alkaline pH such that a normallysolid homopolymer of trifluorochloroethylene is produced and recoveringhomopolymer thus produced as a product of the process.

2. The process of claim 1 in which said water soluble salt of a peracidis a perborate.

3. The process of claim 1 in which said water soluble salt of a peracidis a percarbonate.

4. A process for polymerizing trifluorochloroethylene to produce anormally solid homopolymer which comprises polymerizingtrifluorochloroethylene monomer in a reaction zone in admixture with anamount of water between about 1 and about 10 times the amount of monomerat a temperature between about 0 C. and about 40 C. at a pressuresufficient to maintain monomer in the liquid phase in the presence of aninorganic water soluble salt of a weak peracid as substantially the solepromoting agent in an amount between about 0.003 and about 0.1 molarpercent, maintaining an alkaline pH, maintaining an average residencetime of monomer in the reaction zone of between about 5 and about 50hours such that a normally solid homopolymer of trifluorochloroethyleneis produced, maintaining a conversion of at least 30 percent andrecovering homopolymer thus produced as a product of the process.

5. A process for polymerizing trifluorochloroethylene to produce anormally solid homopolymer which comprises polymerizingtrifiuorochloroethylene monomer in a reaction zone in admixture with anamount of water between about 1 and about 10 times the amount of monomerat a temperature of about 0 C. and about 30 C. and at a pressuresufiicient to maintain monomer in the liquid phase in the presence of analkali perborate as substantially the sole promoting agent in an amountbetween about 0.003 and about 0.07 molar percent, maintaining analkaline pH, maintaining an average residence time of monomer in thereaction zone between about 5 and about 35 hours such that a normallysolid homopolymer of trifluorochloroethylene is produced, andmaintaining a conversion of at least 30 percent and recoveringhomopolymer thus produced as a product of the process.

References Cited in the file of this patent UNITED STATES PATENTS2,296,403 Renfrew et a1 Sept. 22, 1942 2,393,967 Brubaker Feb. 5, 19462,435,537 Ford et al. Feb. 3, 1948 2,531,134 Kropa Nov. 21, 19502,569,524 Hamilton Oct. 2, 1951 2,600,202 Caird June 10, 1952 2,613,202Roedel Oct. 7, 1952 2,689,241 Dittman et a1 Sept. 14, 1954 FOREIGNPATENTS 465,520 Great Britain May 3, 1937 922,429 France June 3, 1947OTHER REFERENCES Hohenstein et al.: India Rubber World 110, 291-294, 300(1944).

1. A PROCESS FOR POLYMERIZING TRIFLUOROCHLOROETHYLENE TO PRODUCE ANORMALLY SOLID HOMOPOLYMER WHICH COMPRISES POLYMERIZINGTRIFLUOROCHLOROETHYLENE MONOMER IN ADMIXTURE WITH AN AMOUNT OF WATERBETWEEN ABOUT 1 AND ABOUT 10 TIMES THE AMOUNT OF WATER BETWEEN ABOUT 1AND CIENT TO MAINTAIN MOMONER IN THE LIQUID PHASE IN THE PRESENCE OF ANINORGANIC WATER SOLUBLE SLAT OF A WEAK PERACID AS SUBSTANTIALLY THE SOLEPROMOTING AGENT, AND MAINTAINING AN ALKALINE PH SUCH THAT A NORMALLYSOLID HOMOPOLYMER OF TRIFLUOROCHLORETHYLENE IS PRODUCED AND RECOVERINGHOMOPOLYMER THUS PRODUCED AS A PRODUCT OF THE PROCESS.